1. Field of the Invention
The subject invention relates to a detection apparatus for dislodging particles from clothing and skin of a person and then testing the dislodged particles for the presence of substances of interest.
2. Description of the Related Art
Detection systems exist for detecting traces of materials, such as narcotics and explosives. Such systems are marketed by Ion Track Instruments, Inc. and are shown, for example, in U.S. Pat. No. 5,491,337.
Prior art detection systems rely upon the fact that trace amounts of contraband will be transferred to the body of a person who handled the contraband, and subsequently will be transferred from the body to any article that the person may carry. These trace amounts of contraband may be collected for analysis by wiping a small sheet of appropriate material across a purse, suitcase or other article that has been handled by a suspect. The prior art sheet then is inserted into a prior art detection apparatus which tests for the presence of certain contraband.
Attempts have been made to provide such contraband testing without physically contacting the suspect or articles that the suspect may be transporting. Several such prior art devices employ a portal through which the suspect will walk. Most of these prior art devices create a flow of air in the portal in an effort to entrain the particles of interest in a continuously flowing air stream. The air stream then is directed to a detector which attempts to identify the presence of particles of interest. Unfortunately, the prior art apparatus draws a significant volume of air from outside the portal, and hence substantially dilutes the concentration of particles of interest in the air stream that is directed to the detector.
U.S. Pat. No. 6,073,499 shows a recent improvement with respect to portals for detecting the presence of contraband on a suspect. More particularly, U.S. Pat. No. 6,073,499 discloses a portal detection system that relies upon the fact that a boundary of air adjacent to a human being is heated by the body. The heated air in this boundary layer is less dense than air further from the suspect, and hence will flow upwardly. Thus, a human thermal plume is created naturally around the human suspect. Particles of interest will be entrained in this thermal plume and will rise upwardly around the body. The portal system shown in U.S. Pat. No. 6,073,499 relies upon this natural phenomena by providing a fan or other air flow generator at a location above the suspect and operating at a speed to substantially match the airflow rate of the naturally-occurring human thermal plume. Thus, the fan or other such device shown in U.S. Pat. No. 6,073,499 merely directs the naturally occurring human thermal plume to a detector without drawing significant volumes of ambient air into the detector. Thus, the concentration of particles of interest is significantly higher than the concentration in prior art portals that create a significant artificial airflow in an effort to entrain and transport the particles of interest.
The prior art detection portal disclosed in U.S. Pat. No. 6,073,499 is particularly effective for detecting trace amounts of contraband that may have been deposited on the skin of a suspect. However, microscopic particles of contraband also are very likely to be trapped in the clothing of a suspect. The natural thermal plume existing in the boundary layer surrounding a human suspect may not be capable of dislodging particles of interest from the clothing. Of course, most of a human suspect will be covered by clothing. Hence, the efficiency of the system disclosed in U.S. Pat. No. 6,073,499 may be limited somewhat by the tendency of particles of interest to be trapped in the clothing of the human suspect passing through the portal.
Some prior art systems, including the system shown in U.S. Pat. No. 6,073,499 suggest the use of air jets to dislodge particles of interest from clothing. However, air jets can create turbulence that may disrupt the efficient upward flow of air in the natural thermal plume surrounding the human suspect. Additionally, air jets have the potential of creating air flow patterns that will draw significant volumes of air from the ambient surroundings, thereby reducing the concentration of the particles of interest in the flow of air directed to the detector.
In view of the above, an object of the subject invention to provide a portal trace detection system that is capable of detecting embedded particles, such as particles embedded in clothing of a human suspect passing through the portal.